Positive active material for rechargeable lithium battery, preparing method thereof and rechargeable lithium battery including the same
A positive active material for a rechargeable lithium battery includes a first positive active material including a secondary particle formed by aggregation of a plurality of primary particles, wherein at least a portion of the primary particles have a radially arranged structure, and a second positive active material including a secondary particle formed by aggregation of a plurality of primary particles, wherein the first positive active material and the second positive active material are both (e.g., simultaneously) nickel-based positive active materials, a particle diameter of the secondary particle of the first positive active material is larger than a particle diameter of the secondary particles\ of the second positive active material, and the second positive active material is coated with a boron compound.
1 . A positive active material for a rechargeable lithium battery, the positive active material comprising:
a first positive active material comprising a secondary particle in which a plurality of primary particles are aggregated, wherein at least one portion of the primary particles aggregated in the secondary particle has a radially arranged structure, and
a second positive active material comprising a secondary particle in which a plurality of primary particles are aggregated,
wherein,
the first positive active material and the second positive active material are both nickel-based positive active materials,
a particle diameter of the secondary particle of the first positive active material is larger than a particle diameter of the secondary particle of the second positive active material, and
the second positive active material is coated with a boron compound, the second positive active material comprising:
a first boron coating portion on an outer surface of the secondary particle, and
a second boron coating portion present on surfaces of the primary particles inside the secondary particle, and the second boron coating portion is in an internal portion of the secondary particle that is inaccessible by effluent if washed with water,
wherein the first boron coating portion is about 70 wt % to about 98 wt % and the second boron coating portion is about 2 wt % to about 30 wt %, each based on a total amount of the first boron coating portion and the second boron coating portion.
2 . The positive active material of claim 1 , wherein in the first positive active material, the primary particles are plate-shaped primary particles, and at least some of the plate-shaped primary particles have a long axis arranged in a radial direction.
3 . The positive active material of claim 2 , wherein an average length of the plate-shaped primary particles in the first positive active material is about 0.01 μm to about 5 μm.
4 . The positive active material of claim 1 , wherein:
the particle diameter of the secondary particle of the first positive active material is about 7 μm to about 25 μm, and
the particle diameter of the secondary particle of the second positive active material is about 1 μm to about 9 μm.
5 . The positive active material of claim 1 , wherein the first positive active material comprises a compound represented by Chemical Formula 1:
Li a1 Ni x1 M 1 y1 M 2 1-x1-y1 O 2 , and Chemical Formula 1
wherein, in Chemical Formula 1, 0.9≤a1≤1.8, 0.3≤x1≤1, 0≤y1≤0.7, and M 1 and M 2 are each independently selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and a combination thereof.
6 . The positive active material of claim 1 , wherein the first positive active material is about 50 wt % to 90 wt % and the second positive active material is about 10 wt % to about 50 wt %, each based on a total amount of the first positive active material and the second positive active material.
7 . The positive active material of claim 1 , wherein the first boron coating portion and the second boron coating portion each comprise boron oxide, lithium boron oxide, or a combination thereof.
8 . The positive active material of claim 1 , wherein the first boron coating portion is about 80 wt % to about 95 wt % and the second boron coating portion is about 5 wt % to about 20 wt %, each based on the total amount of the first boron coating portion and the second boron coating portion.
9 . The positive active material of claim 1 , wherein the first boron coating portion is about 0.02 wt % to about 0.3 wt % based on 100 wt % of the second positive active material.
10 . The positive active material of claim 1 , wherein the second boron coating portion is about 0.001 wt % to about 0.05 wt % based on 100 wt % of the second positive active material.
11 . The positive active material of claim 1 , wherein the second boron coating portion is about 0.001 wt % to about 0.01 wt % based on 100 wt % of the second positive active material.
12 . The positive active material of claim 1 , wherein a total amount of the first boron coating portion and the second boron coating portion is about 0.1 mol % to about 3 mol % based on 100 mol % of the second positive active material.
13 . The positive active material of claim 12 , wherein the total amount of the first boron coating portion and the second boron coating portion is about 0.1 mol % to about 1.3 mol % based on 100 mol % of the second positive active material.
14 . The positive active material of claim 1 , wherein the second positive active material comprises a compound represented by Chemical Formula 11:
Li a11 Ni x11 M 11 y11 M 12 1-x11-y11 O 2 , and Chemical Formula 11
wherein, in Chemical Formula 11, 0.9≤a11≤1.8, 0.3≤x11≤1, 0≤y11≤0.7, and M 11 and M 12 are each independently selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, F, Fe, Mg, Mn, Mo, Nb, P, S, Si, Sr, Ti, V, W, Zr, and a combination thereof.
15 . A method of preparing the positive active material of claim 1 , the method comprising:
mixing a first nickel metal composite hydroxide and a lithium raw material, and heat-treating the resultant to prepare a first positive active material,
mixing a second nickel metal composite hydroxide, a lithium raw material, and a boron raw material, and heat-treating the resultant to prepare a second positive active material, and
mixing the first positive active material and the second positive active material.
16 . The method of claim 15 , wherein a content of the boron raw material is about 0.1 mol % to about 3 mol % based on 100 mol % of the second nickel metal composite hydroxide.
17 . The method of claim 15 , wherein after the mixing of the second nickel metal composite hydroxide, the lithium raw material, and the boron raw material, the heat-treating of the resultant is performed at a temperature of about 650° C. to about 850° C. for about 5 hours to about 25 hours.
18 . A rechargeable lithium battery comprising:
a positive electrode comprising the positive active material of claim 1 ,
a negative electrode, and
an electrolyte.